Starts and runs great in closed loop. After a few minutes white smoke at idle until driven and what I believe to be excess diesel fuel is burned off.

What is the condition of your glow plugs? I assume what you call closed and open loop is actually tuning with or without afterglow?

You’re not giving much info. It can be poor combustion in a worn engine that isn’t warmed up. How many miles? What condition is the engine?

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Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (116k)
1991 350SD (206k)
1991 300D (228k)
2008 ML320 CDI (199k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (267k)

Past Diesels:
1983 300D (228K), 1985 300D (233K), 1993 300D 2.5T (338k), 1993 300SD (291k)

I would not worry about it then. May be just some condensation.

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Jim